The present invention relates to a DC power supply and, more particularly, to a current foldback circuit for a DC power supply.
DC power supplies are universally used to supply a steady state DC voltage--for example, five volts or seven volts--to power an electronic circuit. Invariably, such DC power supplies receive power at another voltage, either a DC voltage at a different steady or variable voltage level or an AC voltage. Because the function of DC power supplies is thus to convert from one voltage to another, they are conventionally called "converters".
Power converters may be classified as being regulated or unregulated. Unregulated converters produce an output voltage which is dependent upon output current; regulated converters produce an output voltage which is, to some degree, independent of the output current. An example of a regulated power converter is disclosed in the German Auslegeschrift No. 27 08 021.
Within the class of regulated power converters are the so-called "switching" converters: power converters which are capable of switching between one power level and another. Typically, such converters continuously monitor their own output voltage and current to sense an overload condition. In case of an overload, the output voltage is reduced by a prescribed amount. Such switching converters include a "current foldback circuit" which triggers a reduction in output voltage when the output current reaches a fallback level, typically 25-50% above the rated current.
In switching converters having a current foldback circuit, the "foldback current" or current level at which foldback occurs, must be substantially greater than the rated current. Current foldback circuits known in the art are unable to discriminate low percentages above rated current. Such circuits are also relatively complex and expensive.